Long-range and local crystal structures of the Sr1−xCaxRuO3 perovskites

The crystal structures of the $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{Ru}{\mathrm{O}}_{3}(0\ensuremath{\le}x\ensuremath{\le}1)$ perovskites are investigated using both long-range and local structural probes. High-resolution synchrotron powder x-ray-diffraction characterization at ambient temperature shows that the materials have orthorhombic long-range crystal structures to high precision, and we support previous work showing that $\mathrm{C}{\mathrm{a}}^{2+}$ substitution for $\mathrm{S}{\mathrm{r}}^{2+}$ primarily changes the tilting of rigid corner-sharing $\mathrm{Ru}{\mathrm{O}}_{6}$ octahedra at their shared oxygen vertices. X-ray pair-distribution function analysis for $\mathrm{SrRu}{\mathrm{O}}_{3},\mathrm{CaRu}{\mathrm{O}}_{3}$, and one intermediate composition show them to display monoclinic symmetry at the local level; when averaged over different domain orientations this yields orthorhombic symmetry in the long range, and no long-range or local phase transitions are observed between 80 and 300 K for materials with intermediate compositions. High-resolution transmission electron microscopy shows that the Sr/Ca distribution is random at the nanoscale. We plot magnetic characteristics such as the ferromagnetic $T\text{c}$, Curie-Weiss theta, effective moment, and ambient temperature susceptibility vs the octahedral tilt and unit-cell volume.